1. Field of the Invention
This invention relates to a rotating spraying type coating apparatus capable of providing a variety of coating patterns.
2. Description of the Prior Art
In a conventional rotating spraying type coating apparatus, a cylindrical or bell-shaped spraying head is attached to the rotary shaft of a rotating drive device, a paint supplying passage is connected to the base end of the spraying head, a paint radiating part is formed at the top end of the spraying head, and air jetting holes for jetting a flow of air to bend forwardly the direction of the paint particles radiated from the paint radiating part are arranged in the form of a circular ring. The coating pattern is changed by controlling (increasing or decreasing) the flow rate of air jetted from the air jetting holes.
However, even if the flow rate of air is greatly changed (0 to 500 1/min), the coating pattern remains annular (like a doughnut), and the width of the coating pattern is not greatly changed. That is, with the conventional coating apparatus, the range of adjustment of the coating pattern is small, and it is impossible to provide an elliptic or dumbbell-shaped coating pattern.
In order to vary the coating pattern, a rotating spraying type coating apparatus has been proposed in which a number of air jetting holes are provided at the outside portion of the spraying head, and the air jetted from the air jetting holes are directed towards the periphery of the spraying head (Japanese Laid-Open Utility Model Publication No. 25270/1979). The conventional coating apparatus is intended to control the velocity and the width of the air flow formed forwardly of the outer circumferential wall of the spraying head in the circumferential direction of the spraying head thereby to control the scattering of the paint particles radiated from the spraying head. However, when the paint particles are radiated from the spraying head, it is considereably difficult because of the following reasons to control the scattering direction of the paint particles with the above-described air flow:
(1) The paint particles have relatively large kinetic energy. Therefore, in order to change the flying direction (or scattering direction) thereof, it is necessary to form an air flow large in velocity or in width.
(2) In order to cover all the paint particles scattered from the spraying head with the air flow satisfying the above-described condition (1), it is necessary to jet a considerably large quantity of air.
(3) The circle formed by the air jetting holes is large in diameter. Therefore, the coating apparatus is necessarily bulky and heavy.
(4) Some of the paint particles radiated from the spraying head stick to the parts adjacent to the air jetting holes, thus causing spitting. In order to eliminate this difficulty, it is necessary to position the air jetting holes at the rear of the spraying head, which makes it necessary to jet a large quantity of air for controlling the coating pattern.
On the other hand, in order to form an elliptic coating pattern, a rotating spraying type coating apparatus has been proposed which comprises; a number of first air jetting holes arranged in the form of a circle; and second air jetting holes for jetting air flows to bend the air flows jetted from the first air jetting holes (Japanese Laid-Open Patent Publication No. 180460/1982 and Japanese Laid-Open Utility Model Publication No. 127762/1984). In the conventional coating apparatus, the annular air flow formed forwardly of the spraying head is caused to collide with another air flow so that the velocity and the width of the air flows are controlled in the circumferential direction of the spraying head, whereby the scattering of the paint particles sprayed radially from the spraying head is controlled. Thus, its fundamental technical concept is completely the same as that of the coating apparatus disclosed by Japanese Laid-Open Utility Model Publication No. 25270/1979. Accordingly, the coating apparatus has the same difficulties, being not practical.
On the other hand, a rotating spraying type coating apparatus with a wash shroud has been known in the art which comprises: an air motor; a bell-shaped spraying head serving also as an electrode and mounted on the rotary shaft of the air motor; a paint supplying passage connected to the base end of the spraying head; a paint radiating part formed at the top end of the spraying head; an air jetting device in annular form installed at the top end of the case of the air motor to jet an air flow towards the rear outside surface of the spraying head; and a wash shroud covering the outside of the spraying head and being movable forwardly and rearwardly to collect a washing agent injected to the spraying head during washing. At the time of coating, the wash shroud is set at the rearward position where the paint radiating part of the spraying head projects from an opening in the front end of the wash shroud; and at the time of washing, the wash shroud is disposed at the forward position where the paint radiating part of the spraying head is held within the wash shroud.
However, in the case of the coating apparatus thus contructed, even if the flow rate of air jetted from the air jetting device is greatly changed, 0 to 500 1/min, the coating pattern remains annular (like a doughnut), and the dimensions of the coating pattern are not greatly changed. That is, the range of adjustment of the coating pattern is small. It goes without saying that it is impossible for the conventional coating apparatus to provide relatively flat coating patterns such as for instance elliptic or dumbbell-shaped coating patterns.
If it is possible to obtain relatively flat coating patterns in addition to circular coating patterns such as annular or disc-shaped coating patterns, in coating a rectangular area with paint the amount of paint wasted is minimized, and the coating operation can be achieved with high efficiency.